Image display system and image display methods

ABSTRACT

An image display system produces a color image by arranging a color shutter capable of time-divisionally switching a plurality of colors to be displayed, in front of a monochrome image display. This image display system comprises: a self-luminous image display part for time-divisionally displaying monochrome images corresponding to three primary colors; and a color display part for time-divisionally coloring and outputting the monochrome images which formed on the side of the light outgoing surface of the self-luminous image display part and which correspond to the three primary colors. The color display part further comprises: a liquid crystal cell driven by carrying out an optical switching on the basis of the inversion between positive and negative polarities; a transparent electrode formed by dividing the liquid crystal cell into a plurality of parts; and a liquid crystal color shutter capable of optionally setting display colors for a plurality of display regions by means of the transparent electrode, the liquid crystal color shutter displaying different display colors for at least two display regions in an optional time in a driving condition.

BACKGROUND OF THE INVENTION

The present invention relates generally to an image display system forproducing a color image by arranging a color shutter capable oftime-divisionally switching a plurality of colors to be displayed, infront of a monochrome image display, and an image display method usingthe image display system.

As a method for displaying a color image, it is usually well carried outto synthesize images of red (R), green (G) and blue (B), which are threeprimary colors of light, or to divide the images. Such an imagesynthesizing method for displaying images is divided into a spacesharing display for two-dimensionally arranging dots for R, G and B tospatially arrange an image, and a time sharing display for displaying R,G and B images in time series. Typically, color cathode ray tubes andliquid crystal displays use the space sharing display since R, B and Gpixels are two-dimensionally arranged. Similarly, in the case of animage pickup, there are adopted methods for spatially arranging R, G andB color filters and for providing a color filter, which is capable ofchanging display colors in time series, in front of an image pickupelement. A process for displaying an image will be briefly describedbelow.

The time sharing display is achieved by quickly switching display colorson the whole display surface in synchronism with the display for R, Gand B images by means of R, G and B color filters or the like. It isnecessary for the time sharing display to switch the display for imagesat a higher speed than three times as high as that in the spatialsharing display. However, it is not necessary for the time sharingdisplay to divide a pixel into parts for R, G and B images, so that itis possible to achieve a higher definition image. As a method forswitching the display color, there is known a method for mechanicallyrotating a disc-like color filter which is divided into equal threeparts and which is color-coded. As a method for electrically switchingthe display color, Bos, et al. proposes a technique in Japanese PatentPublication No. 4-49928, which discloses a so-called liquid crystalcolor shutter, which comprises two liquid crystal cells and colorpolarizing plates arranged on both sides thereof, for switching ON/OFFof the liquid crystal cells to control the plane of polarization forlight to select the wavelength of light absorbed into the polarizingplates to display R, G and B. This liquid crystal color shutter hasadvantages in that there are no mechanical operations, the area of thecolor shutter can be equal to the area of the display screen to reducerequired space, and so forth.

In the liquid crystal color shutter, the absorption axes of a pluralityof color poling plates are perpendicular to each other. The two liquidcrystal cells are turned ON and OFF to directly transmit the polarizedlight of an incident light or to rotate the polarized light by 90degrees to transmit or absorb specific wavelength components, so that adesired display color can be obtained. One of conventionally proposedliquid crystal color shutters is a PI cell having a bend alignment. Thiscan achieve a higher response speed than that of a TN (twisted nematic)cell, which is generally used as a liquid crystal display, i.e., aresponse time of about 2 ms.

On the other hand, in the case of the time sharing display, there iscaused a so-called “color breakup” interference wherein the profile of adisplay image appears to be iridescent due to observer's blink, themovement of observer's eye, the movement of an object on a dynamicimage, and so forth. In order to reduce the color breakup interference,it is desired to increase the switching speed for R, G and B to switchR, G and B as much as possible in a predetermined period of time such asone field period. For example, in the case of a triple speed display fordisplaying each of subfields R, G and B once in one field period, thedisplay period for each color is 1/(60 Hz×3)=5.6 ms assuming that onefield is 60 Hz. Here, one field period is defined as a period necessaryfor completing one color picture in spite of interlace or non-interlacedisplay. For example, one field corresponds to 60 Hz in the case of anNTSC (National Television System Committee) color system for performingthe interlace display.

However, if the frequency of subfields R, G and B displays in one fieldperiod is intended to increase in order to more reduce the color breakupinterference, the response speed of the PI cell is not sufficient asshown in FIG. 1, so that it is required to provide a switching elementhaving a higher response time. For example, when each of subfields R, G,B is displayed twice in a field of 60 Hz, the subfield period for eachcolor is 1/(60×6)=2.8 ms. When 2 ms serving as a response time of the PIcell is subtracted from the display period for each color, it ispossible to ensure only 800 μs, which is 28% of the whole display periodfor each color, as an appropriate display time.

As described above, in the case of the conventional time sharing typedisplay system using the liquid crystal color shutter, there areproblems in that the cell itself of the liquid crystal color shutterdoes not have a sufficient response time, so that a color breakupinterference is caused.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to eliminate theaforementioned problems and to provide an image display system and imagedisplay method, which can ensure a sufficient response time of cells ofa liquid crystal color shutter in a time sharing display system forreducing a color breakup interference.

In order to accomplish the aforementioned and other objects, accordingto a first aspect of the present invention, there is provided an imagedisplay system for producing a color image by arranging a color shuttercapable of time-divisionally switching a plurality of colors to bedisplayed, in front of a monochrome image display, the image displaysystem comprising: self-luminous image display means fortime-divisionally displaying monochrome images corresponding to threeprimary colors; and color display means for time-divisionally coloringand outputting the monochrome images which formed on the side of a lightoutgoing surface of the self-luminous image display means and whichcorrespond to the three primary colors, the color display meanscomprising a liquid crystal cell driven by carrying out an opticalswitching on the basis of the inversion between positive and negativepolarities of the applied voltage, a transparent electrode formed bydividing the liquid crystal cell into a plurality of parts, and a liquidcrystal color shutter capable of optionally setting display colors for aplurality of display regions by means of the transparent electrode, theliquid crystal color shutter displaying different display colors for atleast two display regions in an optional time in a driving condition.

According to a second aspect of the present invention, in the imagedisplay system according to the first aspect, the self-luminous imagedisplay means is monochrome luminescent display means for displaying amonochrome image by a line scanning, the monochrome luminescent displaymeans comprising at least one of a monochrome CRT (Cathode Ray Tube), amonochrome EL (Electro-Luminescent) display element, an FED (FieldEmission Display) and a PDP (plasma display element), which have afrequency F necessary to display all of screens corresponding to thethree primary colors, and the monochrome luminescent display elementhaving a phosphor having an 1/10 afterglow time which is a reducing timeτ, in which a peak density of luminescent becomes 1/10, meeting thefollowing relationship:τ≦{(¼−⅓n)/NF−T}/2assuming that the liquid crystal color shutter has n divided displayregions, a frequency for repeatedly displaying three primary colors fora field period 1/F derived from the frequency F being N, and a responsetime of the liquid crystal color shutter being T.

According to a third aspect of the present invention, in the imagedisplay system according to the first aspect, the liquid crystal colorshutter displays four colors including red, green and blue in each fieldperiod, and the total of display periods for each color in each fieldperiod is equal to each other.

According to a fourth aspect of the present invention, in the imagedisplay system according to the third aspect, a fourth display colorother than the red, green and blue are displayed in switching periodsbetween the red, green and blue.

According to a fifth aspect of the present invention, there is providedan image display method for producing a color image using an imagedisplay system wherein a color shutter capable of time-divisionallyswitching a plurality of colors to be displayed is arranged in front ofa monochrome image display, the image display method comprising a stepof time-divisionally displaying monochrome images corresponding to threeprimary colors using self-luminous image display means; and a step oftime-divisionally coloring and outputting the monochrome images, whichare formed on the side of a light outgoing surface of the self-luminousimage display means and which correspond to the three primary colors,using color display means; wherein the time-divisionally displaying stepfurther includes a sub-step of optionally setting display colors for aplurality of display regions by means of a transparent electrode whichis driven by carrying out an optical switching on the basis of theinversion between positive and negative polarities and which is formedby dividing a liquid crystal cell forming the color display means into aplurality of parts; and a sub-step of displaying different displaycolors for at least two display regions in an optional time in a drivingcondition, using a liquid crystal color shutter formed by thetransparent electrode.

According to a sixth aspect of the present invention, in the imagedisplay method according to the fifth aspect, the self-luminous imagedisplay means is monochrome luminescent display means for displaying amonochrome image by a line scanning, the monochrome luminescent displaymeans comprising at least one of a monochrome CRT, a monochrome ELluminescent display element, an FED and a plasma display element, whichhave a frequency F necessary to display all of screens corresponding tothe three primary colors, and the monochrome luminescent display elementhaving a phosphor having an 1/10 afterglow time τ meeting the followingrelationship:τ≦{(¼−⅓n)/NF−T}/2assuming that the liquid crystal color shutter has n divided displayregions, a period for repeatedly displaying three primary colors for afield period 1/F derived from the frequency F being N, and a responsespeed of the liquid crystal color shutter being T.

According to a seventh aspect of the present invention, in the imagedisplay method according to the fifth aspect, the liquid crystal colorshutter displays four colors including red, green and blue in each fieldperiod, and the total of display periods for each color in each fieldperiod is equal to each other.

According to an eighth aspect of the present invention, in the imagedisplay method according to the seventh aspect, a fourth display colorother than the red, green and blue are displayed in switching periodsbetween the red, green and blue.

Furthermore, the liquid crystal cell according to the first or fifthaspect may be a liquid crystal cell of spontaneous polarization, such asan FLC (ferroelectric liquid crystal) or an AFLC (antiferroelectricliquid crystal) cell, or a liquid crystal cell having a chiral smecticliquid crystal or a DHF (deformed helix ferroelectric liquid crystal).

Moreover, the processing speed may increase as the variation of thefrequency N for repeating the display for the three primary colorsaccording to the second or sixth aspect. It is possible to achievetriple speed when N=1, sixfold speed when N=2, and ninefold speed whenN=3 in comparison with a field frequency in a time sharing display.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a diagram showing a driving method for displaying an image bymeans of a conventional liquid crystal color shutter;

FIG. 2A is a graph showing a desired value of a CRT phosphor afterglowcharacteristic on various driving conditions of an image display systemaccording to the present invention, on the basis of the relationshipbetween sharing number n and afterglow permissible time, and FIG. 2B isa graph showing the desired value of the afterglow characteristic on thebasis of the relationship between the number N of cycles and afterglowpermissible time;

FIG. 3A is a schematic side view of the first preferred embodiment of animage display system according to the present invention, and FIG. 3B isa front view thereof;

FIG. 4A is a perspective view showing the shutter operation principle ofan antiferroelectric liquid crystal cell of a liquid crystal colorshutter in the first preferred embodiment of an image display systemaccording to the present invention, and FIG. 4B is a characteristicdiagram thereof;

FIG. 5A is a table showing the relationship between display colors andazimuths of a polarization axis (absorption axis) of a polarizing plateof a liquid crystal color shutter in the first preferred embodiment, andFIG. 5B is a characteristic diagram thereof;

FIG. 6A is a table showing the correspondence relationship between thepolarities of voltages applied to a liquid crystal cell and R, G and Bdisplays in the first preferred embodiment, and FIG. 6B is acharacteristic diagram showing the transmittance characteristic of aliquid crystal color shutter when R, G, B are displayed;

FIGS. 7A and 7B are front views showing display screens of the firstpreferred embodiment of an image display system according to the presentinvention;

FIG. 8 is a time chart showing operation timings in a driving method forthe first preferred embodiment of an image display system according tothe present invention;

FIG. 9 is a diagram showing the phase relationship between R, G and Bdisplay periods in the first preferred embodiment of a liquid crystalcolor shutter according to the present invention, and the electron beamscanning of a CRT;

FIG. 10 is a diagram showing a problem when a liquid crystal colorshutter is driven without the division of a screen thereof;

FIGS. 11A and 11B are front views of a display screen of the secondpreferred embodiment of an image display system according to the presentinvention, and FIG. 11C is a diagram for explaining a driving methodthereof;

FIG. 12 is a diagram for explaining a drive for one field when thenumber N of cycles is 3;

FIG. 13A is a schematic diagram showing a conventional liquid crystal (πcell) and driving voltages applied to liquid crystal cells 1 and 2, andFIG. 13B is a schematic diagram showing an AFLC according to the presentinvention and driving voltages applied to liquid crystal cells 1 and 2;and

FIG. 14A is a diagram showing the scroll order of color at time A, FIG.14B is a diagram showing the scroll order of color at time B, and FIG.14C is a timing chart showing the driving conditions of a liquid crystalcolor shutter at times A and B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the accompanying drawings, the preferred embodiments ofan image display system and an image display method according to thepresent invention will be described below. Before describing thepreferred embodiments referring to the accompanying drawings, the basicconcept of the present invention will be described.

In an image display system and an image display method according to thepresent invention, means for time-divisionally displaying monochromeimages may include all monochrome luminescent display elements fordisplaying monochrome images using the line scanning, such as whitelight emission monochrome CRTs, monochrome EL emission display elements,FEDs and plasma display elements.

According to the present invention, color display means comprises atleast two liquid crystal cells having a liquid crystal of spontaneouspolarization, such as ferroelectric and antiferroelectric liquidcrystals, and a liquid crystal color shutter of chromatic colorpolarizing plates capable of absorbing only a light component of aspecific visible wavelength region on the absorption axis thereof, or aliquid crystal color shutter using a so-called guest-host (GH) liquidcrystal cell wherein a dichroic pigment is mixed in a liquid crystallayer of spontaneous polarization, such as ferroelectric andantiferroelectric liquid crystals.

The principle of the liquid crystal color shutter using the chromaticcolor polarizing plates is described in detail, e.g., in Japanese PatentPublication No. 4-49928 which discloses that the retardation of a liquidcrystal cell can provide two states per one cell and four states per twocells by switching the voltage applied state and that the three primarycolors, R, G and B, can be displayed using three states out of the fourstates.

The three primary display method is achieved by the fact that when alight is transmitted through a liquid crystal, the polarized statethereof is changed by the retardation of the liquid crystal toselectively switch visible light components absorbed into a chromaticcolor polarizing plate provided in an optical path. A plurality ofchromatic color polarizing plates are combined with each other so as tohave a polarization axis perpendicular to those of other chromatic colorpolarizing plates. The retardation of the ferroelectric orantiferroelectric liquid crystal cell is set so that the polarizationaxis of one of the polarizing plates is parallel to that of the otherpolarizing plate on a certain voltage applied condition and at an angleof 45 degrees to that of the other polarizing plate on the other voltageapplied condition.

The central wavelength of the retardation is preferably set in the rangeof from 450 nm to 580 nm. With such an optical configuration, theincident polarized light is transmitted through the incident sidepolarizing plate without modulation on the former condition and whilethe plane of polarization thereof is rotated by 90 degrees on the lattercondition.

In the case of the GH liquid crystal color shutter, the GH liquidcrystal cell may have a three-layer structure of dichroic pigments ofcyanogen, magenta and yellow, or a three-layer structure of dichroicpigments of red, green and blue, to achieve the operation of a liquidcrystal color shutter. These liquid crystal layers may have amacromolecule structure. In the GH liquid crystal color shutter, analignment of the liquid crystal is selected by a polarity of appliedvoltage to perform switching. For example, in the case of displaying thered, the GH liquid crystal color shutter of R, G and B makes a Red layerbe colored and Green and Blue layers be transparent or translucentFurthermore, in the case of the GH liquid crystal color shutter of cyan,magenta and yellow, the color shutter makes the cyan layer betransparent and magenta and yellow layers be colored.

It is desired to apply a positive polarity on one of the voltage appliedconditions and a negative polarity on the other voltage appliedcondition. For example, R color is displayed by applying +V(V) to afirst liquid crystal cell and +V to a second liquid crystal cell, and Gcolor is displayed by applying +V to the first liquid crystal cell and−V to the second liquid crystal cell. Similarly, B color is displayed byapplying −V to the first liquid crystal cell and +V to the second liquidcrystal cell. All of the display periods for these R, G and B displaycolors are preferably equal to each other.

The condition where −V is applied to both of the first and second liquidcrystal cells remains. On this condition, any colors may be displayed.However, in order to cause an average applied voltage to be zero in onefield period, which includes at least one cycle for displaying R, G andB, to prevent a dc voltage causing sticking from being applied to eachliquid crystal cell, the remaining display state (which will behereinafter referred to as a K display state) preferably has a periodequal to each of the R, G and B display periods, i.e., one field period.For example, assuming that the R, G and B display periods arerepresented by [R], [G], [B] periods and the K display period dividedinto equal three parts is represented by [K/3], the display sequence fordisplaying each of R, G, B once in one field is, e.g., [R], [K/3], [G],[K/3], [B], [K/3]. The display sequence of [R], [G], [B] may beoptionally changed.

The above described display sequence is switched in synchronism with,e.g., the electron beam scanning of a monochrome CRT. For example, whenan R screen is scanned, the liquid crystal color shutter causes R to bedisplayed. In this case, the electron beam interlace-scans ornoninterlace-scans from the left-upper to the right-lower on the screenviewed from the observer. Assuming that the liquid crystal color shutteris not divided and that the whole screen of the liquid crystal colorshutter is switched all at once, the screen can not be scanned in the[K/3] period in which an undesired display color is displayed.Therefore, it is required to divide the screen of the liquid crystalcolor shutter into a plurality of regions in vertical directions of thescreen to carry out the scroll display switching in synchronism with thescanning of the electron beam.

The timings of the scanning period for the electron beam and the displayperiod for the liquid crystal color shutter will be considered. Forexample, the period [R] necessary to display R in a certain displayregion for the liquid crystal color shutter includes a scanning periodwherein an R image is scanned on the corresponding CRT screen region byan electron beam, and an afterglow period wherein a phosphor is emittinglight. Therefore, when the screen is updated at a certain fieldfrequency, a display period [R] determined by the number of repeatedsets of R, G and B displays in one field period must include an electronbeam scanning period in a predetermined display region, and a period inwhich the afterglow of the phosphor emitting light by the scanningdisappears.

Assuming that the afterglow time characteristic of the phosphordecreases exponentially, the relationship between the permissible timefor 1/10 afterglow time that the emission intensity of the phosphorattenuates to 1/10, and the construction and driving conditions of theliquid crystal color shutter is derived. Assuming that a field frequencyis F (Hz), one field period is 1/F (s). Assuming that the number ofcycles for switching R, G and B displays in the period of 1/F is N(e.g., when N=2, the R, G and B displays are repeated twice so as to beRGBRGB), the repeat period for one set of R, G and B is 1/NF (s). Asdescribed above, in the case of a ferroelectric or antiferroelectricliquid crystal cell, it is required to carry out the K display otherthan the R, G and B displays within the period of 1/NF, so that thedisplay period for each of R, G and B is ¼NF (s). On the other hand, ifthe display region of the liquid crystal color shutter is divided intoequal n parts, the period necessary to scan each of R, G and B images ineach display region is ⅓nNF assuming that a fly back period isdisregarded approximately. Assuming that the 1/10 afterglow time of thephosphor is τ (s), the 1/100 afterglow time that the intensity ratio is−40 dB when the attenuation of the emission intensity appears to besubstantially completed, is 2τ. If this is enjoined by the responsespeed T of the liquid crystal, the driving condition to be derived is¼NF≧⅓nNF+2τ+T. That is, the permissible time for the 1/10 afterglow timeof the phosphor is given by τ≦{(¼−⅓n)/NF−T}/2. For example, when F=60Hz, N=1, n=5 division, and T=0.3 ms, then the condition for the 1/10afterglow time τ is τ≦1.37 ms. FIG. 2 shows the relationship between thesharing number n of the display screen, the number N of cycles fordisplaying the R, G and B in one field period, and the 1/10 afterglowpermissible time of the phosphor meeting the condition that theafterglow intensity is −40 dB.

Referring to the accompanying drawings, the preferred embodiment of animage display system according to the present invention will bedescribed in detail below. However, the image display system accordingto the present invention should not be limited to any one of thepreferred embodiments which will be described below, and the inventionmay include various combinations of the constructions of the preferredembodiments.

First, referring to FIGS. 3A and 3B, the first preferred embodiment ofan image display system according to the present invention will bedescribed. FIG. 3A is a schematic side view of the first preferredembodiment of an image display system according to the presentinvention, and FIG. 3B is a front view thereof. In the first preferredembodiment, a liquid crystal color shutter 101 comprisesantiferroelectric liquid crystal cells 102 and 103, and polarizingplates 104, 105, 106, 107 and 108. Assuming that the optical axis inlongitudinal directions of a screen viewed from the front of the screen(in directions in which the polarizing plate 107 is viewed from the sideof the polarizing plate 104) is A and the optical axis in lateraldirections of the screen is A′, one of phase advancing axes F of theantiferroelectric liquid crystal is at an angle of 45 degrees to A andA′. A monochrome CRT 109 is provided tightly on the back of the liquidcolor shutter.

FIGS. 4A and 4B show the shutter operation principle of theantiferroelectric liquid crystal 102 or 103 of the liquid crystal colorshutter 101. Assuming that the polarized light transmitting axis of anachromatic color (neutral gray) polarizing plate 201 is P, and if thephase advancing axes F are set to be at angles of 0 degree (90 degrees)and 45 degrees to the polarized light transmitting axis P when voltagesV of positive and negative polarities are applied to theantiferroelectric liquid crystal cell 102 or 103, the phase of theincident light is not modulated when a voltage of negative polarity isapplied, and the plane of polarization is rotated by 45 degrees when avoltage of positive polarity is applied. Therefore, as shown in thegraph, the shutter operations for transmission and absorption of theincident light can be achieved by selecting the polarity of the appliedvoltage.

FIGS. 5A and 5B shows the relationship between the display colors andazimuths of polarization axes (absorption axes) of the polarizing plates104 through 108 forming the liquid color shutter in the first preferredembodiment. As shown in FIG. 5A, the display colors of the polarizingplates are determined on the basis of the wavelength region of lightabsorbed or transmitted in a visible wavelength region. The polarizingplate 104 absorbs light of the whole visible wavelength region since itis an achromatic color polarizing plate. The transmittance of each ofother chromatic color polarizing plates 105 through 108 on theabsorption axis thereof is shown in FIG. 5B. Although the transmittancecharacteristic on the side of the transmission axis is not shown in thegraph, the transmission characteristics of all of the polarizing platesare substantially uniform over the whole visible region.

FIGS. 6A and 6B show the transmittance characteristics when R, G and Bare displayed, as the correspondence relationship between the polaritiesof voltages applied to the liquid crystal cells 102 and 103 and the R, Gand B displayed by the liquid crystal shutter 101, on the conditions ofthe constructions and azimuths of the polarizing plates in FIGS. 5A and5B. When a voltage of positive polarity is applied to the liquid crystalcell 102 and a voltage of negative polarity is applied to the liquidcrystal cell 103, a black display (which will be referred to as “black”for convenience although it is practically dark brown in this preferredembodiment) is obtained as a fourth display color other than R, G and B.

FIGS. 7A and 7B are front views of display screens in the firstpreferred embodiment of an image display system according to the presentinvention. FIG. 7A shows display regions capable of separatelydisplaying R, G and B in the liquid crystal color shutter 101. Thedisplay regions comprise substantially equal six regions in the firstpreferred embodiment. Each of the display regions 401 through 406 canoptionally display any one of R, G and B by dividing one of transparentelectrodes of the liquid crystal cells 102 and 103 into stripescorresponding to the display regions and by independently applyingvoltage thereto. On the other hand, as shown in FIG. 7B, the CRT 109 issequentially scanned from the left-upper to the right-lower of thescreen similar to the usual CRT screen scanning, to display a monochromeimage for each of R, G and B.

FIG. 8 is a timing chart showing the driving timing in a driving methodfor the first preferred embodiment of an image display system accordingto the present invention. In this image display system, since each of R,G and B images is displayed once in one field period (60 Hz) as shown by501, the number N of cycles for switching the display for R, G and Bis 1. If a part of the display regions in FIG. 7A, e.g., the displayregion 401, is noticed, the driving timing of the liquid crystal colorshutter 101 is shown by 501 through 503, and the driving timing of theCRT 109 is shown by 504 and 505.

That is, the liquid crystal color shutter displays R, G and B as shownby 501, in synchronism with R, G and B images produced by the CRT asshown by 504. In order to avoid the sticking of the liquid crystal colorshutter due to the application of a dc voltage, black serving as thefourth display color is displayed in the latter half of the displayperiod for each of R, G and B. That is, [R: red], [K: black], [G:green], [K: black], [B: blue] and [K: black] are displayed on thedisplay region 401 of the liquid crystal color shutter 101 in that orderin one field period. The characteristics of voltages applied to theliquid crystal cells 102 and 103 are shown by 502 and 503, respectively,in accordance with the polarities of voltages applied to the liquidcrystal cells as shown in FIG. 6A.

Actually, one field period includes six transient response periodperiods T˜0.3 ms of the liquid crystal. Since the ratio of each of theR, G and B display periods to the black display period is selected to be3:1, the voltage applied periods for positive and negative polarities ofvoltages applied in one field period are equal to each other. Therefore,no dc components are continuously applied to the liquid crystal cell, sothat the deterioration of display due to sticking and so forth is notcaused.

On the other hand, on the side of the CRT 109, the beam scanning on apart corresponding to the display region 401 causes white phosphors tobe luminous. The emission intensity of the phosphors on the displayregion 401 in the display periods for the R, G and B images as shown by504 is shown by 505 in FIG. 8. The emission form for each of the displayperiods for the R, G and B images is divided into an emission form for aperiod, in which a CRT display region corresponding to the displayregion 401 is scanned by an electron beam, and an emission form for anafterglow period, in which the emission intensity gradually attenuateswhile another display region is scanned after the scanning of thedisplay region 401 is completed. In the image display system of thepresent invention, when the display of the liquid crystal color shutter101 is switched from the R display to the black display, the emissionintensity of the phosphor is preferably less than −40 dB to the emissionintensity in the scanning period. In the case of the first preferredembodiment, the display region is divided into equal six parts (n=6),and the field frequency is 60 Hz. Therefore, assuming that the responsespeed of the liquid crystal cell is T=0.3 ms, and if the afterglow timeof the phosphor approximates using an exponential function, the 1/10afterglow time τ of the white phosphor capable of being used for the CRT109 is τ≦1.47 ms.

FIG. 9 shows the phase relationship between the R, G and B displayperiods in the liquid crystal color shutter 102 for the display regions401 through 406 shown in FIG. 7A and the electron beam scanning of theCRT 109. FIG. 9 schematically shows time in lateral directions andvertical positions on the screen in vertical directions. As the electronbeam scans from the left-upper to the right-lower on the screen, the R,G and B displays on the liquid color shutter 102 sequentially carriesout scroll operation so that the phase relationship shown in FIG. 8 isheld in each of the display regions 401 through 406. At this time, aplurality of display colors are always displayed on the screen of theliquid crystal color shutter 102 in order to minimize the fly backperiod (shown by dotted lines in the drawing) at the vertical sweep ofan electron beam to prevent a beam sweep quiescent time from beingcaused. If the liquid crystal color shutter is driven by such atechnique, some images are always displayed on the CRT screen in aperiod other than the blanking period necessary for the fly back periodto prevent the beam sweep quiescent time from being caused as shown inFIG. 10, so that the brightness of the screen is hardly deteriorated.

The second preferred embodiment of an image display system according tothe present invention will be described below.

FIGS. 11A, 11B and 11C are diagrams for explaining the second preferredembodiment.

FIGS. 11A and 11B are front views showing the scanning positions on ascreen in scanning periods 702, 702, respectively, and FIG. 11C is aschematic diagram showing the relationship between the R, G and Bdisplay periods in the liquid crystal color shutter and the electronbeam scanning positions on the CRT. The second preferred embodiment ischaracterized in that the number N of cycles for switching R, G and B inone field period is 2. Therefore, in the image display system in thispreferred embodiment, the number N of cycles is N=2, and the speed perone field is sixfold speed. Other constructions are the same as those inthe image display system in the first preferred embodiment.

In this case, R, G and B images scan twice for each image, i.e., sixtimes in total, so that it is possible to prevent the horizontalfrequency from increasing although the vertical frequency is twice aslarge as that in the first preferred embodiment. Therefore, theinterlace scanning is carried out for each of the first scanning 701 andthe second scanning 702 so that the scanning positions are interpolatedin another. In the second preferred embodiment, if the field frequencyis 60 Hz which is the same as that in the first preferred embodiment,the 1/10 afterglow permissible time τ of the phosphor is τ≦0.66 ms sinceN=2. Since other constructions, operations and advantages are the sameas those in the image display system in the first preferred embodiment,the duplicate explanations are omitted.

Finally, as an example where the number N of cycles is 3, the thirdpreferred embodiment of an image display system according to the presentinvention is shown in FIG. 12. In this preferred embodiment, as shown inFIG. 12, the number N of cycles is 3, and the speed per one field isninefold speed. Thus, the present invention may be applied to the casewhere N=3 as shown in FIG. 12, not only the case where N=2 shown in FIG.11C.

Furthermore, in the above described second and third preferredembodiments, the number N of cycles has been 2 or 3 to provide sixfoldor ninefold speed, the present invention should not be limited to suchmultiples of 3, but the invention may be applied to, e.g., fivefoldspeed. For example, the fivefold speed (not shown) can be easilyachieved by setting “n=1 at F=100 Hz” or “N=2 at F=50 Hz” whendisplaying [R], [G], [B], [R] and [G] in a period of 1/60 Hz.

Referring to FIG. 13B, the driving principle of the above describedliquid crystal color shutter according to the present invention will bedescribed as compared with that of a conventional π cell shown in FIG.13A. As described above, the two liquid crystal cells are prepared inthe color shutter, and the voltages applied to the two liquid crystalcells are switched to produce a plurality of states. In the conventionalπ cell, the voltages applied to the cells are switched between apositive (+) or negative (−) voltage and no voltage as shown in FIG. 13Ato produce respective colors.

On the other hand, in the case of the operation principle of the liquidcrystal color shutter according to the present invention, each of thevoltages applied to the liquid crystal cells 1 and 2 is switched between+V and −V, and the voltages applied to the liquid crystal cells 1 and 2are combined as shown in FIG. 13B to produce predetermined operationstates so as to provide an R period when the voltage applied to theliquid crystal cell 1 is +V and the voltage applied to the liquidcrystal cell 2 is +V, a G period when the voltage applied to the liquidcrystal cell 1 is −V and the voltage applied to the liquid crystal cell2 is −V, a B period when the voltage applied to the liquid crystal cell1 is −V and the voltage applied to the liquid crystal cell 2 is +V, anda black (K) period when the voltage applied to the liquid crystal cell 1is +V and the voltage applied to the liquid crystal cell 2 is −V.

Referring to FIGS. 14A through 14C, the timings for driving the colorshutter using the liquid crystal cells 1 and 2 driven at the drivingtiming shown in FIG. 13B will be described. For example, the displaycolors of the color shutter in time A are G, K, R and R as shown in FIG.14A, and the display colors of the color shutter in time B are G, G, Kand R as shown in FIG. 14B. If the times A and B are superposed on thedriving timings of the color shutter, the timing can be obtained asshown in FIG. 14C.

As can be clearly seen from the description for FIG. 13B, while thepresent invention has been applied typically to a color liquid crystalshutter having liquid crystal cells of spontaneous polarization, such asferroelectric and antiferroelectric liquid crystal cells, the presentinvention should not be limited thereto, but the invention may beapplied to all of color liquid crystal shutters for carrying out opticalswitching operations on the basis of the inversion between positive andnegative polarities. Therefore, the present invention may include chiralsmectic liquid crystals and DHFs capable of being driven by suchswitching operations although the chiral smectic liquid crystals andDHFs.

As described in detail above, according to the present invention, it ispossible to provide a liquid crystal display system which has lessfaults, such as color breakup interference, than those in an imagedisplay system using a conventionally proposed liquid crystal colorshutter and which has a high display brightness and an enhanced quality.

1. An image display system for producing two-dimensional color images,comprising: a self-luminous white/black image display fortime-divisionally displaying white/black two-dimensional imagescorresponding to three primary colors by self-emitting alone, saidself-luminous image display including a controller for controlling aswitching between a light emitting state and non-light emitting state,and a luminous surface for displaying two-dimensional images byconverting electric signals corresponding to image data into opticaldata; a color shutter configured to be colored by at least three primarycolors and for time-divisionally switching a plurality of colors to bedisplayed, provided in front of said luminous surface of saidself-luminous white/black image display, said color shutter including aplurality of liquid crystal cells arranged over an entire displaysurface and having a plurality of display parts forming portions of theentire display surface and configured to change optical features of eachof said plurality of display parts, and transparent electrodes formed onsaid entire display surface and configured to supply a voltage to atleast two display parts of said plurality of display parts by convertingpositive and negative polarities; wherein said color shutter isconfigured to optically set display colors for said plurality of displayparts and to be driven by a scroll driving, and to display a differentcolor image on each of said display parts in an optical time in adriving condition, so that said transparent electrodes supply a constantvoltage having a positive or negative polarity to said liquid crystalcells during a period of displaying a certain color; and wherein saidself-luminous white/black image display on which displayed images aretwo-dimensional is provided on its surface with said color shutter. 2.An image display system as set forth in claim 1, wherein each of saidliquid crystal cells of said color shutter has a ferroelectric oranti-ferroelectric liquid crystal of spontaneously polarization.
 3. Animage display system as set forth in claim 1, wherein each of saidliquid crystal cells of said color shutter has a chiral smectic liquidcrystal or a DHF for switching a potential state between at least twopotential states to carry out an optical switching.
 4. An image displaysystem as set forth in claim 1, wherein said color shutter displays fourcolors including red, green and blue in each field period, and the totalof display periods for each color in each field period is equal to eachother.
 5. An image display system as set forth in claim 4, wherein afourth display color other than said red, green and blue is displayed inswitching periods between said red, green and blue.
 6. An image displaymethod for producing a two-dimensional color image, comprising:time-divisionally displaying white/black two-dimensional imagescorresponding to three primary colors using a self-luminous white/blackimage display for self-emitting alone, which includes a controller forcontrolling a switching between a light emitting state and a non-lightemitting state, and a luminous surface for displaying two-dimensionalimages by converting electric signals corresponding to image data intooptical data; time-divisionally switching, via a color shutterconfigured to be colored by at least three primary colors and providedin front of said luminous surface of said self-luminous white/blackimage display, a plurality of colors to be displayed, said color shutterincluding a plurality of liquid crystal cells arranged over an entiredisplay surface and having a plurality of display parts forming portionsof the entire display surface and configured to change optical featuresof each of said plurality of display parts, and transparent electrodesformed on said entire display surface and configured to supply voltagesto at least two display parts of the plurality of display parts byconverting positive and negative polarities; and optically setting, viasaid color shutter, display colors for said plurality of display partsby driving by a scroll driving, and displaying a different color imageon each of said display parts in an optical time in a driving condition,so that said transparent electrodes supply the constant voltage having apositive or negative polarity to said liquid crystal cells during aperiod of displaying a certain color; and wherein said self-luminouswhite/black image display on which displayed images are two-dimensionalis provided on its surface with said color shutter.
 7. An image displaymethod as set forth in claim 6, wherein each of said liquid crystalcells has a ferroelectric or anti-ferroelectric liquid crystal ofspontaneous polarization.
 8. An image display method as set forth inclaim 6, wherein each of said liquid crystal cells has a chiral smecticliquid crystal or a DHF for switching a potential state between at leasttwo potential states to carry out an optical switching.
 9. An imagedisplay method as set forth in claim 6, wherein said color shutterdisplays four colors including red, green and blue in each field period,and the total of display periods for each color in each field period isequal to each other.
 10. An image display method as set forth in claim9, wherein a fourth display color other than said red, green and blue isdisplayed in switching periods between said red, green and blue.